Personal computers and other devices use an assortment of memory storage devices. The ideal memory technology should combine high-speed, high-density, non-volatility and low power consumption. Chalcogenide memory is a promising next-generation memory that offers some of these advantages. The term chalcogenide memory is derived from the term for group VI elements of the periodic table also known as chalcogens. Chalcogens include several elements including oxygen, sulfur, selenium, tellurium and polonium. Chalcogenide memory is also referred to as phase-change memory or phase-change chalcogenide memory because the chalcogenide material can switch between a crystalline phase and an amorphous phase. Certain chalcogenide materials exhibit different electrical and optical properties based upon the phase of the material. These differences in properties can be used to represent data where reading the data includes detecting the differences using optical or electronic sensors.
Often, the phase of the chalcogenide material is controlled by applying heat to the material. The duration and amount of heat applied determines the phase of the chalcogenide material (i.e., crystalline or amorphous). One method of applying heat is through the use of electricity. Electrically induced amorphous-crystalline phase transition has been demonstrated to have high-speed (10 ns), long endurance (1012 cycles), low programming energy, and excellent scaling characteristics. Moreover, chalcogenide memory is resistant to ionizing radiation effects. However, current phase-change memory circuits are limited in density due to, among other things, the size of a memory cell necessary for a single bit. Further information on chalcogenide memory circuits can be found in U.S. Pat. No. 6,965,521 to Li et al and U.S. Pat. No. 7,012,273 to Chen, which are fully incorporated herein by reference.
One of the components in determining the size of a memory cell is the size of the phase-change material. For example, larger phase-change material uses additional heat to create a change in phase. The increased heat creates issues with both the power efficiency of the memory device and thermal cross-talk. Thermal cross-talk is a problem that occurs when heat leaks from the memory cell being written to an adjacent memory cell. If the thermal cross-talk is great enough, the data in the adjacent memory cell can be corrupted. Power efficiency is also a factor for dense memory arrays due to issues related to supplying sufficient power to small devices, including issues due to leakage current and excessive heat.
These and other issues have presented challenges to the implementation and design of phase change memory devices, including those involving chalcogenide-based memory and similar applications.